/* 
List of Variables GR -- grain rate, in dollars per 100 Ibs. 
TQG -- total quantity of grain shipped, in tons. 
LAKES -- dummy variable; = 1 if Great Lakes were open to navigation; =O otherwise. 
PO -- cheating dummy variable; = 1 if colluding reported by Railway Review; =O otherwise. 
PN -- estimated cheating dummy variable. 
DM1 -- =1 from week 28 in 1880 to week 10 in 1883; =O otherwise; reflecting entry by the Grand Trunk Railway 
DM2 -- = 1 from week 1 l to week 25 in 1883; =O otherwise; reflecting an addition to New York Central. 
DM3 -- = 1 from week 26 in 1883 to week I I in 1886; =O otherwise; reflecting entry by the Chicago and Atlantic. 
DM4 -- = I from week 12 to week 16 in 1886; =O otherwise; reflecting departure of the Chicago and Atlantic from the JEC. 
*/